Detection: O365 Mailbox Folder Read Permission Assigned

Description

The following analytic identifies instances where read permissions are assigned to mailbox folders within an Office 365 environment. It leverages the o365_management_activity data source, specifically monitoring the ModifyFolderPermissions and AddFolderPermissions operations, while excluding Calendar, Contacts, and PersonMetadata objects. This activity is significant as unauthorized read permissions can lead to data exposure and potential information leakage. If confirmed malicious, an attacker could gain unauthorized access to sensitive emails, leading to data breaches and compromising the confidentiality of organizational communications.

1`o365_management_activity` Workload=Exchange (Operation=ModifyFolderPermissions OR Operation=AddFolderPermissions) Workload=Exchange object!=Calendar object!=Contacts object!=PersonMetadata 
2| eval isReadRole=if(match('Item.ParentFolder.MemberRights', "(ReadAny)"), "true", "false")  
3| rename UserId as user  
4| stats count earliest(_time) as firstTime latest(_time) as lastTime by Operation, user, object, Item.ParentFolder.MemberUpn, Item.ParentFolder.MemberRights 
5| `security_content_ctime(firstTime)` 
6| `security_content_ctime(lastTime)` 
7| `o365_mailbox_folder_read_permission_assigned_filter`

Data Source

No data sources specified for this detection.

Macros Used

Name Value
o365_management_activity sourcetype=o365:management:activity
o365_mailbox_folder_read_permission_assigned_filter search *
o365_mailbox_folder_read_permission_assigned_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1098 Account Manipulation Persistence
T1098.002 Additional Email Delegate Permissions Privilege Escalation
KillChainPhase.EXPLOITAITON
KillChainPhase.INSTALLATION
NistCategory.DE_CM
Cis18Value.CIS_10
HAFNIUM
Lazarus Group
APT28
APT29
Magic Hound

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Notable Yes
Rule Title %name%
Rule Description %description%
Notable Event Fields user, dest
Creates Risk Event True
This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events.

Known False Positives

Mailbox folder permissions may be configured for legitimate purposes, filter as needed.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
A folder was granted read permission by $user$ 42 70 60
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation Passing N/A N/A N/A
Unit Passing Dataset o365 o365:management:activity
Integration ✅ Passing Dataset o365 o365:management:activity

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range


Source: GitHub | Version: 3